It will be appreciated by those having ordinary skill in the art that conventional aqueous dyeing processes for textile materials, particularly hydrophobic textile fibers, generally provide for effective dyeing, but possess many economic and environmental drawbacks. Particularly, aqueous dyebaths which include organic dyes and dyeing assistants must be disposed of according to arduous environmental standards. Additionally, heat must be applied to dry the textile material after dyeing in an aqueous bath. Compliance with environmental regulations and process heating requirements thus increase the costs of aqueous textile dyeing to both industry and the consuming public alike. Accordingly, there is a long-felt need in the art for an alternative dyeing process wherein such problems are avoided.
One alternative to aqueous dyeing that has been proposed in the art is the dyeing of textile materials, including hydrophobictextile fibers like polyester, in a supercritical fluid. Particularly, textile dyeing methods using SCF--CO.sub.2 have been explored.
However, those in the art who have attempted to dye textile materials, including hydrophobic textile fibers, in SCF--CO.sub.2 have encountered a variety of problems. These problems include, but are not limited to, "crocking" (i.e. tendency of the dye to rub off when the dyed article is touched) of the dyed textile article; unwanted deposition of the dye onto the article and/or onto the dyeing apparatus during process termination; difficulty in characterizing solubility of the dyes in SCF--CO.sub.2 ; difficulty introducing the dyes into the SCF--CO.sub.2 flow; and difficulty in preparing the dyes for introduction into the dyeing process. These problems are exacerbated when attempts to extrapolate from a laboratory dyeing process to a commercial scale process are made.
There have been several attempts in the prior art to address the problems associated with dyeing of textile materials, particularly hydrophobic textile fibers, in SCF--CO.sub.2. One such attempt is described in Patent Publication No. WO 97/13915 published Apr. 17, 1997, inventors Eggers et al., assignee Amann and Sohne GMBH & Co. This publication describes a process for dyeing a textile substrate, particularly polyester yarns, using SCF--CO.sub.2. The process includes a pressure and/or temperature decrease and/or volume enlargement as part of the termination of the process. The described process attempts to provide a dyed textile substrate having a high color-fastness level. However, this goal is pursued by removal of dye material from the fluid so that in the final stage of the process a fluid largely free from residual dye flows against or through the dyed textile substrate. Thus, complex additional systems, such as a secondary circulation system, are required to provide dye-free fluid to the process.
Moreover, dye-free fluid can be supplied to the autoclave or first circulation system associated with the autoclave before or during execution of the pressure decrease, temperature decrease, and/or volume enlargement. Thus, there is a lack of criticality associated with the timing of the incorporation of the dye-free fluid into the system, as well as a lack of criticality associated with whether a pressure decrease, temperature decrease, and/or volume enlargement is selected for process termination. Finally, the spent sorbent material requires disposal after process termination, which can create environmental concerns analogous to those encountered with the use of conventional aqueous dyeing processes.
Poulakis et al., Chemiefasern/Textilindustrie, Vol. 43-93, February 1991, pages 142-147 discusses the phase dynamics of SCF--CO.sub.2. An experimental section describing an apparatus and method for dyeing polyester in SCF--CO.sub.2 in a laboratory setting is also presented. This method is thus believed to be limited in practical application.
U.S. Pat. No. 5,199,956 issued to Schlenker et al. on Apr. 6, 1993 describes a process for dyeing hydrophobic textile materials with disperse dyes by heating the disperse dyes and textile material in SCF--CO.sub.2 with azo dyes having a variety of chemical structures. The patent thus attempts to provide an improved SCF--CO.sub.2 dyeing process by providing a variety of dyes for use in such a process.
U.S. Pat. No. 5,250,078 issued to Saus et al. on Oct. 5, 1993 describes a process for dyeing hydrophobic textile materials with disperse dyes by heating the disperse dyes and textile material in SCF--CO.sub.2 under a pressure of 73 to 400 bar at a temperature in the range from 80.degree. C. to 300.degree. C. Then the pressure and temperature are lowered to below the critical pressure and the critical temperature, wherein the pressure reduction is carried out in a plurality of steps.
U.S. Pat. No. 5,578,088 issued to Schrell et al. on Nov. 26, 1996 describes a process for dyeing cellulose fibers or a mixture of cellulose and polyester fibers, wherein the fiber material is first modified by reacting the fibers with one or more compounds containing amino groups, with a fiber-reactive disperse dyestuff in SCF--CO.sub.2 at a temperature of 70-210.degree. C. and a CO.sub.2 pressure of 30-400 bar. Specific examples of the compounds containing amino groups are also disclosed. Thus, this patent attempts to provide level and deep dyeings having very good fastness properties by chemically altering the fibers prior to dyeing in SCF--CO.sub.2.
U.S. Pat. No. 5,298,032 issued to Schlenker et al. on Mar. 29, 1994 describes a process for dyeing cellulosic textile material with disperse dyes, wherein the textile material is pretreated with an auxiliary that promotes dye uptake subsequent to dyeing under pressure and at a temperature of at least 90.degree. C., with a disperse dye from SCF--CO.sub.2. The auxiliary is described as being preferably polyethylene glycol. Thus, this patent attempts to provide improved SCF--CO.sub.2 dyeing by pretreating the material to be dyed.
What is needed, then, is an improved method of dyeing hydrophobic textile fibers with colorant materials in SCF--CO.sub.2 which addresses the problems identified, yet heretofore unsolved, by the art. An improved method of dyeing hydrophobic textile fibers with colorant materials in SCF--CO.sub.2 which resolves the "crocking" problem identified in the art is particularly desired.